In the past with chain saws, as an example, a desired increase of the drive power required an increase of the stroke volume of the drive motor. An increase in the stroke volume produces a very undesirable increase of the weight of the saw.
On the other hand, it is known that a turbo charger can produce a considerable power increase in a four cycle engine without an appreciable increase of the motor weight. Turbo charging has not been applicable, up to now, to two cycle internal combustion engines which run with a gasoline/oil mixture because the lubricant residues contained in exhaust gases would undoubtedly foul a turbo charger with carbon within a very short time and thus it would become useless in a short time.
The object of the present invention is to provide a two cycle internal combustion engine in which, despite the addition of lubricant to the fuel, the use of a turbo charger is possible without problems in operation.
Thus, problems attendant to turbo charging of a two cycle engine are solved, according to the invention by positioning the turbine wheel housing of an exhaust gas turbo charger within the exhaust system.
It is advantageous here if the turbine wheel housing is arranged within an exhaust manifold positioned to communicate directly with the exhaust port. This positioning causes the turbine and its housing to be brought to the desired operating temperature as quickly as possible. Further, it is desirable that the exhaust manifold be fastened directly to a cylinder head, directly at the outlet of an exhaust port passage running through the cylinder head.
To obtain an increased filling of the cylinder, it is also advantageous if the cooling system of the motor is designed, additionally, for the cooling of the compressor housing. It is useful here if the cooling system of the motor is designed for the cooling, additionally, of at least part of the intake manifold system extending between the compressor and the intake port of the motor.
In order to obtain a flatter torque output curve in the operating range of motors intended for chain saws, for example, it may be advantageous if the intake system is so tuned that, in the range from 30 to 10%, especially from 25 to 15%, below the motor RPM corresponding to maximum power, there takes place a dynamic rinsing or scavenging of the cylinder by means of periodic vibrations in the exhaust system.
Engines made in accordance with the present invention are useful in chain saws, lawn mowers and other two cycle engine applications especially where engine weight is an important consideration.
The invention will be explained in detail below from one example of execution represented in the drawing which is a sectioned view of a single cylinder two cycle engine as seen from a plane perpendicular to the cylinder axes.